In the current environment, with the explosion in popularity of the Internet for entertainment, commerce and other new uses (as well as the old uses), many users expect to get large bandwidth data sets, such as the data that makes up a video sequence, transmitted over packet-based networks, one example of which is the Internet. A packet-based network is a network where the data is transmitted in a non-continuous fashion, which allows the physical connection to be shared by multiple users simultaneously. The end-users expect to get such video data in real, or near real, time. Real-time video streams consume considerable bandwidth, as the recipient expects to receive video at its frame rate. Thus, if the frame rate is thirty frames per second, the recipient expects the network to deliver, in one second or less, enough data to decode thirty frames of video.
For some transmission media, such as direct satellite broadcasting systems or cable television networks, sending real-time video is easy and has in fact been done for years. Unfortunately, such networks are only useful where only a few (many numbering in the hundreds) video streams are being sent and they are being sent simultaneously to the recipients, and cannot readily be adapted to sending different video streams at possibly different times, to many different places on the network.
One disadvantage of streaming content out from a centralized source every time that content is requested, even if it is done in non-real-time, is the cost of handling full video connections to each of possibly millions of recipients. With high-bandwidth content and many recipients requesting a copy of the content, the network will slow under the weight of the traffic. One partial solution that attempts to overcome that disadvantage is to have the content streamed once from its source at a central location to many servers located nearer to recipients, thus reducing the number of copies of the data that have to flow over large portions of the network. While this solution would be useful if the content that is streamed to the network edge is used by recipients near each edge server, even more network bandwidth might be wasted as unused content is streamed from the central location to edge servers that might not ever serve up the content.